Loudspeaker construction



Aug. 30, 193 E. E. WICQERSHA 2,128 722 LOUDSPEAKER CONSTRUCTION Filed001;. 29, 1934 INVENTOR.

Patented Aug. 30, 1938 UNITED STATES PATENT OFFlCE LOUDSPEAKERCONSTRUCTION Elmer E. Wickersham, San Leandro, Calif. ApplicationOctober 29, 1934, Serial No. 750,511

' 4 Claims. (01. 179- 1155) This application is a continuation in part,as to all matters common to the two, of my pending application entitled:Electric transformer and core construction, Serial No. 663,298, filedMarch My invention relates to the construction of and to the characterand kind of material I choose to use in the magnetic units ofloudspeakers and other similar devices.

Objects An object of this invention is to construct the core memberormembers of the magnetic units of loudspeakers and similar devices ofmagnetite or what is commonly known as black sand.

Another object is to produce a practically closed magnetic circuit inthe magnetic core units of loudspeakers and sound reproducers of anon-corrosive finely divided metal which may be formed, or poured dryinto a coil housing to form a magnetic unit, which is easily and cheaplyconstructed.

Another object is to provide a core member for loudspeakers and similardevices of a metallic material which is naturally in a finely dividedstate.

Another object is to produce a magnetic circuit of finely dividednon-corrosive metal in its natural state, having high magneticproperties and whose contact resistance between its various meta1particles is high enough to reduce to a minimum any eddy currents whichmay be induced therein.

Another object is to produce a loudspeaker,

transducer, or other similar devices, whose magnetic components arecomposed of magnetite, or of that material which is commonly known asblack sand that will reproduce signals truly over the entire audiblescale.

Another object is to produce a magnetic unit for loudspeakers ortransducers and kindred devices, having a moulded core composed ofmagnetite.

Another object is to provide a core member for a loudspeaker ortransducer of magnetite, comprising a plurality of parts having its poleportions positioned intermediate its ends.

Another object is to provide a core member for loudspeakers and kindredinstruments, having the pole pieces thereof intermediate its ends,whereby one of the pole pieces may be placed adjacent one side of thecone or diaphragm and the other of said pole pieces placed adjacent theother side of the cone or diaphragm member of the speaker.

Other objects will appear hereinafter.

I attain these objects by use of the construction illustrated in theaccompanying drawing, in which:

Fig. 1 is a longitudinal section through my 5 loudspeaker or transducer.

Fig. 2 is a transverse section on line 2-2 of Fig. 1.

Fig. 3 is a schematic view showing the direction of coil winding and themagnetic field 10 produced thereby.

One Iorm in which my invention may appear, is illustrated in Fig. 1 inwhich core members are of the moulded type, and the metallic portionthereof being magnetite, or what is common- 15 ly called black sand.

This material is naturally granular, is noncorrosive, has a relativelyhigh resistance, and is generally highly adaptable for use in the makingof cores for magnetic units. no

Due to the nature of this material, it may be mixed with a binder,poured into a form and by allowing the binder to dry or harden, the coreW111 become rigid and self-supporting and readily handled. 5

If it is not desired to make the core rigid, the magnetite may be poureddry into a suitable container or housing and thus form a core for amagnetic unit.

One of the effects of the presence of magnetite 30 in the fiux path of acoil through which current is flowing, is: that for the same number ofturns in a coil, its inductance is increased and, consequently, a coilhaving a core of magnetite will require a lesser number of turns tor thesame 35 inductance and thus reduce the ohmic resistance, which isadvantageous.

In addition to these above advantages which are due to the severalcharacteristics of magnetite, a core composed of this material and usedin radio 40 signal sound reproducers will not be greatly affected byhysteresis, and, therefore, a more nearly perfect reproduction of thesound may be had.

Description l9 by screw means 20; said supporting bracket l9 beingattached by screws 2| to sounding board 22.

Sections H-l I of coil B preferably are wound so that when they havetheir inner ends 23 at-- tached together their fields axially of thecoils are opposed. Consequently, the radial flux at the mating oradjacent ends of the coils will be aiding so as to produce a strongradial flux in the air gap 28. The outer ends 24-25 of the coils arebrought outwardly of the enclosure l3 through suitable openings 26-26for connection to a source of power not shown.

It will be noted that one of the sections I or core A has a protrusion21 formed thereon which acts as a spacer between the sections Ill-l0 toform an annular groove 28 between faces 29-30 of sections lO-ID whichconstitute the pole pieces of core A.

Coil 3| is floatingly mounted in groove 28 and has its free ends 32-33extending outwardly of closure l3 through openings 34-35, and areadapted to be connected to a voice current supply (not shown).

Coil 3| has secured thereto a plurality of rod members 36 extendingoutwardly of core A through openings 31 therein and are attached indriving relation to disc or cone 3!! as shown.

Operation The loudspeakers herein disclosed are intended to work uponthe electro-dynamic principle, which is well known in the art.

Briefly: these units employ a magnetic field which is preferablysupplied by a field coil when excited by a direct current.

The field coils core is, in this case, supplied with an air gap formedbetween the faces of the pole pieces.

A movable coil adapted to be excited by an alternating or pulsatingcurrent is fioatingly mounted in said air gap in the fiux path of saidfield coil, and drives the cone or disc to which it is attached whensaid respective coils are excited by the passage of the proper electriccurrent therethrough.

In the operation of a loudspeaker employing my invention, the field coreis practically immune from the effects of eddy currents in the core,caused by the reaction of the magnetic alternating field set up by theenergizing current of the movable, or voice coil, thus reducing to aminimum any distortional effects in reproduction arising from thissource.

Therefore, I claim:

1. An electro-magnetic unit for a transducer, having a field coil and asubstantially cylindrical core therefor, an encircling groove lyinggenerally in a plane radial with respect to the core axis and havingspaced radial walls formed in said core and forming axially spaced polepieces of like polarity, a voice coil between said poles out of contactwith said core, and a driven ele ment attached to said coil, said voicecoil being free to float between said pole pieces except insofar as itis partially restrained by said driven element.

2. An electro-magnetic unit for a transducer, having a field coil and acore therefor, an annular groove formed in said core and having spacedwalls lying in planes substantially normal to the magnetic field axis, amovable coil positioned in said groove between said walls and encirclinga portion of said core defined by a core surface other than either ofsaid spaced walls, and means suspending said movable coil in theposition specified for movements in the direction of the magnetic fieldaxis.

3. In a transducer having a two part field coil, a voice coil, and acore for said field coil, an encircling groove in said core memberintermediate its ends in which the voice coil is suspended out ofcontact with said core, and one part of said two part coil beingpositioned on one side of said groove and the other of said coil partsbeing positioned on the opposite side of the groove.

4. An electro-magnetic unit for a transducer comprising a field coil, acore therefor including an uninterrupted central core portion and anouter core portion formed with a groove encircling said uninterruptedcentral portion, said groove having opposed walls lying in planessubstantially normal to the axis of the central core portion, a flatvoice coil positioned in said groove between said opposed walls andencircling said uninterrupted central core portion but out of contacttherewith, and means suspending said voice coil in said groove formovements therein out of contact with said core.

ELMER E. WICKERSHAM.

